BP Process Safety Series Hazards of Trapped Pressure and Vacuum, 2009

100 صفحه pdf

BP Process Safety Series Hazards of Trapped Pressure and Vacuum, 2009

A collection of booklets describing hazards and
how to manage them

سرفصلها:

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Theory of pressure and vacuum . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Different units of pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Absolute pressure vs. gauge pressure . . . . . . . . . . . . . . . . . . . . 5
1.5 The behaviour of gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.6 Pressure-force relationship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.7 Compressed air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.8 Hydraulic and pneumatic systems . . . . . . . . . . . . . . . . . . . . . . . 12
1.9 Identification of trapped pressure and unexpected
vacuum hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.10 Sources of trapped pressure and vacuum . . . . . . . . . . . . . . . . . 14
2 Hazards of trapped pressure . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1 Breaking containment under pressure . . . . . . . . . . . . . . . . . . . . 15
2.2 Storage tanks are fragile vessels . . . . . . . . . . . . . . . . . . . . . . . . 19
2.3 Blocked/choked/isolated safety valves, vents and drains . . . . . . 25
2.4 Hydraulic legs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.5 Trapped pressure in pigging operations . . . . . . . . . . . . . . . . . . . 38
2.6 Thermal expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.7 Ice or hydrate formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
2.8 Leak and pressure testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
2.9 Hydrostatic testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
2.10 Work permits and isolation certificates . . . . . . . . . . . . . . . . . . . . 62
2.11 Trapped pressure underneath catalyst crust . . . . . . . . . . . . . . . 63
2.12 Trapped pressure in a fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
2.13 Utility/process connections and flexible hoses . . . . . . . . . . . . . . 66
2.14 General advice and safe practices . . . . . . . . . . . . . . . . . . . . . . . 71
3 Hazards of vacuum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
3.1 Ignorance of hazards of ambient pressure . . . . . . . . . . . . . . . . 75
3.2 Blocked/choked/isolated vents and drains . . . . . . . . . . . . . . . . . 77
3.3 Steam condensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
3.4 Ammonia dissolved in water . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
3.5 Management of change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
3.6 Can your vessels deal with vacuum? . . . . . . . . . . . . . . . . . . . . . 85
4 Points to remember . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
Short bibliography for regulations and norms . . . . . . . . . . . 91
Test yourself! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Acronyms and abbreviations . . . . . . . . . . . . . . . . . . . . . . . . 95